Before a received ultra-wide-bandwidth (UWB) signal can be demodulated, a template signal must be aligned with the received signal. The purpose of the alignment is to determine a relative delay of the received signal with respect to the template signal. This process is called signal acquisition.
Conventionally, the alignment is performed by a serial search of possible delay times of cells in an uncertainty region, see Simon et al., “Spread Spectrum Communications Handbook,” McGraw-Hill, N.Y., 1994. Each different search location, i.e., time interval, with respect to time, is called a cell. If the signal exists at a delay location, then that cell is called a signal cell. In that method, the received signal is correlated with the template signal, and an output of the correlation is compared to a threshold. If the output is lower than the threshold, then the template signal is shifted by some amount time. The shifted amount time corresponds usually to a resolvable path interval. This information is then used to repeat the correlation until the output exceeds the threshold.
If the output of the correlation comes from a case where the signal path and the template signal are aligned, it is called a signal cell output, otherwise, it is called a non-signal cell output. A false alarm occurs when a non-signal cell output exceeds the threshold. In that case, time tp elapses until the search recovers. This time is called the penalty time for false alarm.
Due to the short time resolution of UWB signals, serially searching all delay locations can take a long time. Therefore, the alignment method must be fast so that the time allocated for the acquisition of the UWB signal is reduced.
The mean acquisition time of a serial search is directly proportional to the number of cells in the uncertainty region, N, for large N values, see Polydoros et al., “A unified approach to serial search spread-spectrum code acquisition-Part I: General Theory,” IEEE Trans. Comm., Vol. COM-32, pp. 542–549, May 1984. In a general form, FIG. 3 shows the basic operation of the prior art serial cell search of an uncertainty region 300 with a template 301.
Therefore, there is a need for a method and system that can acquire UWB signals in a shorter time than the known prior art serial search techniques.